Two, the letter in this article is 100% legit and genuine, as you can see from the site. There was much debate over whether I should change the contents of the letter to make it more 'believable' than reality, and I'm still on the fence over that.

I was reading and reading and liking that the letter had typos in it because that made it realistic, but thinking that while this was a creative idea it was lacking something and then I saw the URL and my blood froze.

If people make it down to the bottom, that's a real nice punch in the gut. There's officially nothing about this that isn't frightening now. Like, someone dropped something on the floor upstairs just now and I jumped out of my skin.

One remark: the line about the CCTV uses 'it' and I'm not sure if that's referring to the TV or the SCP. I assume, after having read the whole article, that 'it' refers to the object, but that's not clear at the beginning.

Okay, and a second remark: the image of a woman that they use on the homepage of that site freaked me right the hell out, so I wondered why it wasn't the inspiration for the woman's image on the mirror.

Which is why I'm considering rewriting a letter myself. But then that makes me think, which is more important in this site, whether or not the author is fully responsible for the article he/she has written, or simply whether or not the article is good (not that I'm saying this one definitely is). I'm quite on the fence over this right now.

I don't find him using a letter written by someone else any different than what's done with images.
Sure, it's that much neater when someone hacks together something on his own, see Mackenzie's Camera Disruption, but elsewhere taken images work very well, when you provide the fluff around them.
This is pretty much the same thing. And the fluff around it is well done.

Hi, I'm Creek. I helped write this SCP.
About the original letter. I know that since it's been removed, this is kind of a non-issue, but I felt the need to clarify.
We could not credit the original author of this letter, for the reasons stated below.
This letter has attained a certain amount of fame in and about eating disorder circles, as a 'pledge' letter. As in, people are encouraged to copy/paste it, and add their name under 'Worthless One', in order to make public their commitment to their disease. This letter was probably created with that express purpose in mind, and as so, I felt more comfortable knowing that something akin to a meme was being used here, instead of some heartfelt letter from some poor girl, posting on her personal blog.

This is just the tip of the iceberg. There is probably a shaving mirror for the god of muscle builders and a full length mirror for the plastic surgery-obsessed. All these people are psychiatrically ill.

This isn't so much offensive or shocking as …dumb. I'd be interested in hearing reasoning to the contrary, but right now this just reads like "hey what if anorexia was still anorexia BUT MADE BY WIZARDS" … even side-stepping words like "exploitative" (horror is the exploitation of our fears and uncertainties, yadda yadda), that just seems stupid.

Nah.
The odd thing is that the mirror doesn't cause anorexia, in that case i'd downvote for reasons similar to when someone made Krokodil an SCP (people doing this sort of stuff to themselves from their own will is scarier than any sort of magic effect/disease/whatever) it is merely a recipient of a large volume of letters written by people with such.
I suppose it does feel slightly underdeveloped when you consider that the letter's contents are by and large irrelevant to why we contain it, and we'd do the same with a reindeer's horn that received pleas to Santa, but well, the execution is decent, and I still kind of like it.

… that pretty much seems to disqualify it from being an SCP, though. The Foundation can't really afford prolonged study of every odd cultural phenomena or fixation. Do some work? Yes. I just don't think eating disorders qualify… at least not as presented.

Because even if you blurred that line, it's still leaning too heavily on non-original content. SCPs like 173 certainly do some leaning, too, but there's a balance. Each needs the other for maximum effect.

Um, how?
What makes it an SCP is that it inexplicably receives this sort of rants in hard copy.

Now what I'd like to see here is the foundation detaining an author of such a rant, and trying to interview him/her about why did they send anything, or whether they did at all. Depending on how well the interview was handled, this could be very brilliant, even using the above source.

I'm not saying there's zero potential for the topic. The magical-anorexia vibes are in the presentation. The the interview you're describing could very well be interesting, but I wasn't commenting on or criticizing hypothetical ideas.

As-is, the anon letter is the focal point of the article. It bugs me that it's 1) not original, when it would be very easy to write a similar letter, and 2) presumably/maybe written by a real person with an eating disorder.

Actually, it would bug me if the author didn't link in the original , for both reasons.
As of now ,not only he admits to not writing it, straight out, but linking the article to something external gives it a bit more fake credibility, which I like - such things might be very decent as a document drop.

I know you aren't commenting on hypothetical ideas - I was just elaborating on what I think about this object.